A viscoelastic material represented by a macromolecular material such as rubber or elastomer is widely applied to various products such as tires, balls to be used in sports, rolls for printing machines.
In various products composed of the viscoelastic material or a metal material, to save cost and time, development of products by using a simulation are made in various industrial fields. For example, to estimate the restitution performance of a golf ball, simulation methods of actual ball-hitting tests are proposed.
In conducting the simulation, property values of a composing material of a ball measured by a viscoelastic spectrum meter for measuring the rigidity, the viscosity of the material and a tension testing machine for measuring the modulus of longitudinal elasticity (Young's modulus) thereof are used as input data in the simulation. In particular, because the viscoelastic spectrum meter measures the property values of a dynamic strain-applied specimen, the viscoelastic spectrum meter is useful for simulating products composed of the viscoelastic material.
However in measurement conducted by using the viscoelastic spectrum meter and the tension testing machine for measuring the modulus of longitudinal elasticity, a large deformation amount cannot be imparted to the specimen. Thus a maximum strain speed applied to the specimen composed of the viscoelastic material at a measuring time is as low as 0.001/s to 1.0/s and a maximum compression strain is also as low as 0.0001 to 0.02.
A product composed of the viscoelastic material may deform at a high speed and greatly owing to the influence of an external force applied thereto when it is actually used. For example, when the golf ball is hit, a maximum strain speed of a material for the golf ball is as high as 500/s to 5000/s, and a maximum compression strain thereof is as large as 0.05–0.50.
As described above, the viscoelastic spectrum meter and the tension testing machine for measuring the modulus of longitudinal elasticity are incapable of measuring the property values of the viscoelastic material in a condition equivalent to a condition where the product composed of the viscoelastic material deforms quickly and greatly when it is actually used. Thus the maximum strain speed of the viscoelastic material and its maximum compression strain measured at a simulation time are much different from those measured at the time when the product composed of it is actually used. Therefore the conventional simulation method of inputting the property value obtained by using the viscoelastic spectrum meter and the tension testing machine is incapable of accomplishing an accurate simulation by taking the property of the viscoelastic material into consideration.
That is, it is known that the deformation behavior of the viscoelastic material when an impact load is applied thereto is different from that of the viscoelastic material when a static load is applied thereto. That is, the deformation behavior of the viscoelastic material is greatly influenced by a deformation amount or a deformation speed. In particular, when a macromolecular material such as rubber and elastomer is subjected to the impact load, it deforms at a speed as high as several seconds by 10000 or several seconds by 1000 and as greatly as by several tens of percentages in a quantitative respect. There are many viscoelastic materials that deform at such a high speed and in such a large amount. To develop products efficiently, there is a demand for development of a simulation method capable of conducting an accurate simulation. More specifically, the performance of a product such as the golf ball to which an impact is applied when it is used depends on a dynamic behavior in a condition where it deforms at a high speed and greatly. The performance of the product also depends on the characteristic of the material thereof. Therefore to develop a product, it is indispensable to conduct an accurate simulation in a condition equivalent to a condition in which the product composed of the material is actually used.
Some viscoelastic materials change in its property value such as its rigidity (modulus of longitudinal elasticity and modulus of transverse elasticity) and loss coefficient in dependence on the magnitude of a strain and a strain speed when an external force such as an impact load is applied thereto. That is, the viscoelastic material is diverse in its deformation speed and deformation magnitude. Thus depending on the deformation speed and the deformation magnitude, the viscoelastic material has a property that it changes not linearly but highly nonlinearly. More specifically, as the viscoelastic material is deformed by an external force applied thereto and strained increasingly, the loop area of an S-S (strain-stress) curve increases, and the property such as the loss coefficient thereof changes in dependence on a deformation state (speed and magnitude of deformation) thereof, thus showing nonlinearity in its property. Many viscoelastic materials have a high nonlinearity in their properties. Thus there is a demand for development of a simulation method capable of simulating a product composed of such a viscoelastic material.
However there are no methods capable of accurately expressing a phenomenon that the property of the viscoelastic material, for example, its rigidity (modulus of longitudinal elasticity and modulus of transverse elasticity) and loss coefficient changes nonlinearly in a high extent in dependence on the deformation speed and deformation magnitude thereof. Simulations have been hitherto conducted on the assumption that the property value of the viscoelastic material composing the golf ball or the like hardly changes. Consequently the conventional simulation method has a disadvantage that it is incapable of correctly estimating the performance of the product composed of the viscoelastic material in an actual use. Thus to estimate the performance of the product, trial manufacture cannot but be made.
The present invention has been made in view of the above-described situation. Thus, it is an object of the present invention to accurately estimate the performance of a product composed of a viscoelastic material showing nonlinearity in its property, for example, a product composed of a viscoelastic material whose rigidity such as the modulus of longitudinal elasticity changes in dependence on a magnitude of a strain and that of a strain speed, by conducting a simulation in a condition in which the product is actually used.